Discovery of an aurora on Mars

In the high-latitude regions of Earth, aurorae are the often-spectacular visual manifestation of the interaction between electrically charged particles (electrons, protons or ions) with the neutral upper atmosphere, as they precipitate along magnetic field lines. More generally, auroral emissions in planetary atmospheres "are those that result from the impact of particles other than photoelectrons" (ref. 1). Auroral activity has been found on all four giant planets possessing a magnetic field (Jupiter, Saturn, Uranus and Neptune), as well as on Venus, which has no magnetic field. On the nightside of Venus, atomic O emissions at 130.4 nm and 135.6 nm appear in bright patches of varying sizes and intensities, which are believed to be produced by electrons with energy <300 eV (ref. 7). Here we report the discovery of an aurora in the martian atmosphere, using the ultraviolet spectrometer SPICAM on board Mars Express. It corresponds to a distinct type of aurora not seen before in the Solar System: it is unlike aurorae at Earth and the giant planets, which lie at the foot of the intrinsic magnetic field lines near the magnetic poles, and unlike venusian auroras, which are diffuse, sometimes spreading over the entire disk. Instead, the martian aurora is a highly concentrated and localized emission controlled by magnetic field anomalies in the martian crust.     

Interhemispheric asynchrony of the sleep EEG in northern fur seals

Summary In northern fur seals the two brain hemispheres can generate the EEG slow waves during sleep not only simultaneously, as in all the terrestrial mammals investigated, but also independently as in dolphins.     

Inactivation of the Wip1 phosphatase inhibits mammary tumorigenesis through p38 MAPK-mediated activation of the p16(Ink4a)-p19(Arf) pathway

Modulation of tumor suppressor activities may provide new opportunities for cancer therapy. Here we show that disruption of the gene Ppm1d encoding Wip1 phosphatase activated the p53 and p16 (also called Ink4a)-p19 (also called ARF) pathways through p38 MAPK signaling and suppressed in vitro transformation of mouse embryo fibroblasts (MEFs) by oncogenes. Disruption of the gene Cdkn2a (encoding p16 and p19), but not of Trp53 (encoding p53), reconstituted cell transformation in Ppm1d-null MEFs. In vivo, deletion of Ppm1d in mice bearing mouse mammary tumor virus (MMTV) promoter-driven oncogenes Erbb2 (also called c-neu) or Hras1 impaired mammary carcinogenesis, whereas reduced expression of p16 and p19 by methylation-induced silencing or inactivation of p38 MAPK correlated with tumor appearance. We conclude that inactivation or depletion of the Wip1 phosphatase with resultant p38 MAPK activation suppresses tumor appearance by modulating the Cdkn2a tumor-suppressor locus.     

Low density lipoprotein receptor-related protein 1 couples β1 integrin activation to degradation

Low density lipoprotein receptor-related protein (LRP) 1 modulates cell adhesion and motility under normal and pathological conditions. Previous studies documented that LRP1 binds several integrin receptors and mediates their trafficking to the cell surface and endocytosis. However, the mechanism by which LRP1 may regulate integrin activation remains unknown. Here we report that LRP1 promotes the activation and subsequent degradation of β1 integrin and thus supports cell adhesion, spreading, migration and integrin signaling on fibronectin. LRP1 interacts with surface β1 integrin, binds the integrin activator kindlin2 and stimulates β1 integrin–kindlin2 complex formation. Specifically, serine 76 in the LRP1 cytoplasmic tail is crucial for the interaction with kindlin2, β1 integrin activation and cell adhesion. Interestingly, a loss of LRP1 induces the accumulation of several integrin receptors on the cell surface. Following internalization, intracellular trafficking of integrins is driven by LRP1 in a protein kinase C- and class II myosin-dependent manner. Ultimately, LRP1 dictates the fate of endocytosed β1 integrin by directing it down the pathway of lysosomal and proteasomal degradation. We propose that LRP1 mediates cell adhesion by orchestrating a multi-protein pathway to activate, traffic and degrade integrins. Thus, LRP1 may serve as a focal point in the integrin quality control system to ensure a firm connection to the extracellular matrix.     

Interhemispheric asynchrony of the sleep EEG in northern fur seals

In northern fur seals the two brain hemispheres can generate the EEG slow waves during sleep not only simultaneously, as in all the terrestrial mammals investigated, but also independently as in dolphins.     

Human behaviour: Egalitarian motive and altruistic punishment

Altruistic punishment is a behaviour in which individuals punish others at a cost to themselves in order to provide a public good. Fehr and G?chter present experimental evidence in humans indicating that negative emotions towards non-cooperators motivate punishment, which, in turn, provokes a high degree of cooperation. Using Fehr and G?chter's original data, we provide an alternative analysis of their experiment that suggests that egalitarian motives are more important than motives for punishing non-cooperative behaviour. This finding is consistent with evidence that humans may have an evolutionary incentive to punish the highest earners in order to promote equality, rather than cooperation.     

A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO

Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60-100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90-120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of approximately 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80-90 km for which we have no explanation.     

Nonlinear electrophoresis of dielectric and metal spheres in a nematic liquid crystal

Electrophoresis is a motion of charged dispersed particles relative to a fluid in a uniform electric field. The effect is widely used to separate macromolecules, to assemble colloidal structures and to transport particles in nano- and microfluidic devices and displays. Typically, the fluid is isotropic (for example, water) and the electrophoretic velocity is linearly proportional to the electric field. In linear electrophoresis, only a direct-current (d.c.) field can drive the particles. An alternating-current (a.c.) field is more desirable because it makes it possible to overcome problems such as electrolysis and the absence of steady flows. Here we show that when the electrophoresis is performed in a liquid-crystalline nematic fluid, the effect becomes strongly nonlinear, with a velocity component that is quadratic in the applied voltage and has a direction that generally differs from the direction of linear velocity. The new phenomenon is caused by distortions of the liquid-crystal orientation around the particle that break the fore-aft (or left-right) symmetry. The effect makes it possible to transport both charged and neutral particles, even when the particles themselves are perfectly symmetric (spherical), thus allowing new approaches in display technologies, colloidal assembly and separation, microfluidic and micromotor applications.     

树木管胞大小对于西伯利亚南部林草交错带森林生长及环境适应性的指示意义

为了研究木质部细胞、树木个体和森林群落3个尺度之间的关联, 在西伯利亚南部以西伯利亚落叶松(Larix sibirica)和欧洲赤松(Pinus sylvestris)为主的3个采样点37个样地, 测量725根树芯的树木年轮宽度, 采用系统随机的方法选择其中195个树芯进行管胞大小的测量和计算。结果表明, 尽管局地环境和树种组成有所不同, 但在树木个体和森林群落两个水平上, 管胞大小与树木径向生长的年际变化显著相关。较小的平均管胞尺寸指示更低的年际生长量和更高的年际生长波动。平均管胞大小对半干旱区针叶林生境湿度和森林生长适应性具有指示作用, 揭示树木通过调节管胞的大小在生长适应与生长安全性二者间的权衡机制。